1. Field of the Invention
The present invention generally relates to connection restoration in connection-oriented network, and in particular to a method and system which are capable of restoring a point-to-multipoint connection when a fault occurs thereon.
2. Description of the Related Art
A typical example of connection-oriented network where a connection is established according to the source-routing scheme computing a route based on network topology information exchanged between nodes is ATM (asynchronous transfer mode) network. In the ATM network, restoration is conventionally performed taking into account only the case of a point-to-point connection.
In the standardization work done with ATM Forum, the fault recovery techniques of such a point-to-point connection have been proposed by David M. Kushi and Ethan M. Spiegel (AF/97-0391R1 xe2x80x9cSignalling Procedures for Fault Tolerant Connectionsxe2x80x9d ATM Forum, Apr. 27, 1997, pp.13-18, and AF/97-0632 xe2x80x9cProcedures for Fast Connection Recovery in PNNI Networksxe2x80x9d ATM Forum and Jul. 21, 1997 pp.9-17). As a first example, in a network configuration where a source terminal is connected to a node and a destination terminal is connected to another node, these nodes perform connection switching when receiving a message indicating fault occurrence. In a second example, in a network which is logically layered and managed, a logical layer is determined depending on a fault situation and the ingress and egress nodes of the logical layer perform connection switching.
The point-to-multipoint connection techniques has been proposed by Ted Tedijanto et al. in the ATM forum (AF/96-140lR3 xe2x80x9cSupport for Leaf Initiated Join in PNNIxe2x80x9d ATM Forum Jul. 21, 1997 pp.2-30). The point multi-point connection is directed to a connection technique which allows concurrent transmission of data from a single source terminal (hereinafter called a root terminal) to two or more destination terminals (hereinafter called leaf terminals). Some methods are proposed to the point-to-multipoint connection technique.
A basic method is that the root terminal establishes a connection to every leaf terminal. More specifically, the root terminal transmits a SETUP message to a first leaf terminal which is to be initially connected. Thereafter, the root terminal transmits an ADD_PARTY message to a second leaf terminal and the ADD_PARTY message travels over the initial connection to a node at which the initial connection branches to the second leaf terminal. Then, a SETUP message is transmitted from the branching node to the second leaf terminal to establish the connection to the second leaf terminal. In this manner, the point-to-multipoint connection is established.
According to the basic setup method, however, the amount of management information increases with an increase in the number of leaf terminals, resulting in the increasing burden on the root terminal. To reduce the burden on the root terminal, there has been proposed a connection method called Network LIJ (Leaf Initiated Join).
In the Network LIJ connection method, after the connection has been established between the root terminal and the first leaf terminal, a connection request received from a second leaf terminal causes the connection to be established by a proxy root node rather than the root terminal. In other words, nodes including the root terminal upstairs (i.e. in the direction of the root terminal) from the proxy root node have no awareness of the second leaf terminal. It is the same with other leaf terminals.
More specifically, the root terminal sends a SETUP message to the first leaf terminal only when the connection to the first leaf terminal is established. When a point-to-multipoint connection is requested by the second leaf terminal, the second leaf terminal sends a LEAF SETUP REQUEST message to the network. The LEAF SETUP REQUEST message is received by an immediate node (hereinafter called a endpoint node) which is directly connected to the second leaf terminal. When receiving the LEAF SETUP REQUEST message, the endpoint node computes a route to the root terminal to sent it according to the computed route. For each leaf terminal on the Network LIJ connection, a node that initially responds to the LEAF SETUP REQUEST message is determined which is hereinafter referred to as a proxy root node. The proxy root node performs connection setup and management as a substitute for the root terminal. When receiving the LEAF SETUP REQUEST message, the proxy root node sends a SETUP MESSAGE or an ADD PART message to the second leaf terminal to perform the point-to-multipoint connection.
Therefore, no message for connection establishment is sent to nodes upstream from the proxy root node. Since the root terminal has no need to manage leaf terminals other then the first leaf terminal, the burden on the root terminal is dramatically reduced as a result.
However, a conventional restoration method is applied only to the point-to-point connection and the same restoration method cannot be applied to the point-to-multipoint connection. Since a proxy root node sets up a new connection without the intervention of the root endpoint nodes upstream from the proxy root node do not manage the connection. Therefore, when a fault occurs between the root terminal and the proxy root node, neither the proxy root node nor the root node manages the fault connection segment.
Further, there are cases where a plurality of SETUP messages are generated to restore the point-to-multipoint connection when a fault occurs. In this case, it is necessary to determine which message should be selected. For this, there is proposed a method that SETUP messages are numbered in sequence by the nodes and a SETUP message having the latest serial number is selected and used to restore the connection. In the case of point-to-point connection, there is no problem because the root node controls the entire point-to-point connection. However, in the case of Network LIJ point-to-multipoint connection, when a fault occurs between the root terminal and the proxy root node, it is very difficult to manage the serial numbers given to the SETUP messages.
An object of the present invention is to provide a connection restoration method and system which can achieve automatic fault recovery when a fault occurs in point-to-multipoint connection configuration.
Another object of the present invention is to provide a connection restoration method and system which can achieve automatic fault recovery with simplified procedures when a fault occurs in Network LIJ point-to-multipoint connection.
According to an aspect of the present invention, in a connection-oriented network where a point-to-multipoint connection is formed between a terminal which is a sending side of the connection (hereinafter, called root terminal) and a plurality of terminals which are a receiving side of the connection (hereinafter, called leaf terminal) through a plurality of nodes of the network and the point-to-multipoint connection is established and managed in the network without only dependence on the root terminal, at a first node of the nodes, it is determined whether a connection release message caused by a fault of the network is received from root terminal side after a first connection to a leaf terminal has been established in response to a first connection request message received from the leaf terminal. When the connection release message is received from the root terminal side, the first connection to the leaf terminal is maintained. Thereafter, a second connection request message is sent to the network to wait for a connection message for restoration to be received from the network in response to the second connection request message. And a route is switched by connecting the first connection to a second connection determined by the connection message for restoration received from the network.
Further, at a second node located upstream from the first node, it is determined whether the connection release message caused by the fault is received from leaf terminal side and, when the connection release message is received from the leaf terminal side, a third connection to the root terminal is maintained. Thereafter, the connection message for restoration is sent to the leaf terminal side when receiving the second connection request message from the first node, and a route is switched by connecting the third connection to the second connection determined by the connection message for restoration after the second connection has been established.
According to another aspect of the present invention, in a connection-orientated network wherein a point-to-multipoint connection is formed between a terminal which is a sending side of the connection (hereinafter, called root terminal) and a plurality of terminals which are a receiving side of the connection (hereinafter, called leaf terminal) through a plurality of nodes of the network, wherein the point-to-multipoint connection is established and managed by at least one node (hereinafter, called proxy root node) which is determined according to a predetermined procedure, a first connection from a proxy root node affected by a fault of the network to the root terminal is maintained when the fault is detected in the point-to-multi-point connection and a second connection from an endpoint node to the leaf terminal is also maintained, wherein the endpoint node is directly connected to a leaf terminal affected by the fault. In response to a connection request sent by the endpoint node, an alternate route between the proxy root node affected by the fault and the endpoint node is established, and the alternate route is connected to the first connection and the second connection at the proxy root node and the endpoint node, respectively.